An inkjet printing system generally includes a printhead and an ink supply which supplies liquid ink to the printhead. The printhead ejects ink drops through a plurality of orifices or nozzles and toward a print media, such as a sheet of paper, so as to print onto the print media. Typically, the nozzles are arranged in one or more arrays such that properly sequenced ejection of ink from the nozzles causes characters or other images to be printed upon the print media as the printhead and the print media are moved relative to each other.
In general, inkjet inks are either dye-based or pigment-based. Both are typically prepared in an ink vehicle that contains the dye and/or the pigment. Dye-based inkjet inks generally use a colorant which is dissolved in the ink vehicle and pigment-based inks generally use a colorant that is insoluble in the ink vehicle, but suspended or dispersed in the form of small particles.
Perceived color quality of inkjet inks can be characterized using any one of several color space systems, such as Munsell or CIELAB, as is well known in the art. With respect to the Munsell color space, a given color is defined using three terms, namely Hue (H), Value (V), and Chroma (C). With respect to the CIELAB color space, a color is defined using three terms L*, a*, and b*. With the CIELAB system, L* defines the lightness of a color and ranges from 0 (black) to 100 (white). In addition, the terms a* and b* may be used to define the hue and chroma of a color, where a* ranges from a negative number (green) to a positive number (red) and b* ranges from a negative number (blue) to a positive number (yellow). The additional terms of h° (hue angle) and C* (chroma) are also used to further describe a given color, as is known to those skilled in the art. As such, the Munsell H, V, and C values or the CIELAB L*, a*, and b* values can be used to calculate a volume of color space that a specific ink set can produce, whereby the larger the color space volume the more colors the ink set is capable of producing.
Desirable properties of inkjet inks include good crusting resistance, good stability, proper viscosity, proper surface tension, little color-to-color bleed, rapid dry time, no deleterious reaction with printhead components, high solubility of the dyes in the ink vehicle, consumer safety, low strike through, high color saturation, good dot gain, and suitable color characteristics. Furthermore, the durability of the printed image, for example, light and water fastness, also contributes to the quality of a printed inkjet image.
Known inkjet inks may possess one or more of the above described properties. Few inkjet inks, however, possess all of these properties since an improvement in one property often results in the degradation of another property. Accordingly, efforts continue in developing ink formulations that have improved properties while minimizing the degradation of others. However, challenges still remain to further improve the image quality and lighffastness of inkjet inks without sacrificing pen performance and/or reliability.